The present disclosure relates generally to the field of vehicle brake systems. Concretely, an electrohydraulic vehicle brake system with an electromechanical actuator for actuating the brake system is described.
Electromechanical actuators have already been used for some time in vehicle brake systems, for example, for realising an electrical parking brake function (EPB). In the case of electromechanical brake systems (EMB), they replace the conventional hydraulic cylinders at the wheel brakes.
Owing to technical advances, the efficiency of the electromechanical actuators has continually increased. It was therefore considered to use such actuators also for implementing modern driving dynamics control systems. Such control systems include an antilock braking system (ABS), a traction control system (TCS) or an electronic stability program (ESP), also referred to as vehicle stability control (VSC).
WO 2006/111393 A, and corresponding to U.S. Pat. No. 8,540,324 B2, teaches an electrohydraulic brake system having a highly dynamic electromechanical actuator which performs the pressure modulation in the driving dynamics control operation. The electromechanical actuator described in WO 2006/111393 A is provided to act directly on a master cylinder of the brake system. Owing to the high dynamics of the electromechanical actuator, the hydraulic components of the brake system known from WO 2006/111393 A can be reduced to a single 2/2-way valve per wheel brake. To realise wheel-individual pressure modulations, the valves are then actuated individually or in groups in multiplex operation.
However, the minimising to only one valve per wheel brake also results in challenges, such as an undesired pressure equalisation when valves are opened simultaneously. A solution based on a highly dynamic control behaviour is specified for this in WO 2010/091883 A, and corresponding to US Patent Publication No. 2012/013173 A1.
WO 2010/091883 A discloses an electrohydraulic brake system having a master cylinder and a tandem piston accommodated therein. The tandem piston is actuable by means of an electromechanical actuator. The electromechanical actuator comprises an electric motor arranged concentrically with respect to the tandem piston, as well as a transmission arrangement which converts a rotational movement of the electric motor into a translational movement of the piston. The transmission arrangement is composed of a ball screw drive having a ball screw nut coupled in a rotationally fixed manner to a rotor of the electric motor and a ball screw spindle acting on the tandem piston.
A further electrohydraulic brake system having an electromechanical actuator acting on a master cylinder piston is known from WO 2012/152352 A, and corresponding to US Patent Publication No. 2014/197680 A1. This system can operate in a regenerative mode (generator operation).